Incumbent telecommunication providers are using the capabilities of existing and next generation residential high-speed broadband connections to deliver services other than high-speed Internet (HSI) access. These new services include voice (utilizing Voice over IP technology) and streaming video. Such services may be offered at a price premium over and above the existing HSI access, improving the revenue generating capability of providers' network.
Delivering streaming content (e.g. voice and video) requires specialized processing/treatment by the network to ensure acceptable service quality for these new applications. This specialized processing typically involves a Network Element (NE) identifying both the subscriber and the streaming media content and a) ensuring there exists sufficient bandwidth to accept the new service request; b) expediting the delivery of the content; and c) protecting the premium content from unregulated, greedy protocols and applications. Collectively, these functions can be aggregated into an “admission control” element and a “traffic management” element.
Admission control is responsible for identifying the service request and determining whether sufficient network resources exist to allow the request and honor the required quality guarantees. Admission control can be explicit, through techniques such as a signaling protocol (e.g. RSVP, SIP etc) or implicit, by dynamically identifying the service/application in real-time.
Traffic management (TM) is an umbrella term used to describe the allocation of network resources to competing services. It typically includes functions such as traffic queuing and servicing, traffic rate policing and shaping. Traffic management functions can be applied at various levels of granularity—ranging from traffic from individual applications and subscribers, to aggregates that contain traffic of similar classes from hundreds or thousands of users. Depending on the dynamic nature of the network's load, a NE may dynamically manage TM properties in real-time or merely statically provision the TM properties in response to results from the admission control element. A traffic manager implements a resource allocation scheme based on both an implied hierarchy of importance of service types and a model of the current resource availability and allocation. As new service requests are processed, network resources may be allocated or re-allocated, taken from lower priority flows and given to higher priority requests.
Traffic management functions control the bandwidth, packet loss probability, delay and delay variation (jitter) for a given flow of (in this case) IP datagrams (also referred to herein as “packets”). Each service may require a unique combination of these parameters to deliver acceptable service quality, and each service request forces a re-evaluation of the resource allocation policy, potentially re-allocating the resources amongst all the competing flows.
Implicit to both admission control and traffic management is the process of traffic classification. Classification is the process of matching incoming traffic against a database of signatures in order to identify some descriptive property of the traffic—such as who the traffic is from (for subscriber identification) or what type of traffic is being transmitted (service type classification for traffic management). Classification is a necessary and critical component of both admission control and traffic management elements described above.
FIG. 1 depicts a typical topology for a high-speed broadband network. At the service end, services such as video, voice, and Internet access are provided to subscribers 100 via an interface to an access network 102, such as a cable or DSL (Digital Subscription Line) modem 104 and a router 106. Meanwhile, access network 100 is coupled to an aggregation network 108 via appropriate network elements, such as DSLAMs (Digital Subscription Line Access Multiplexer) 110 and 112 and CMTS (Cable Modem Termination System) element 114. An IP network element (NE) 116 is used to couple aggregation network 108 to networks from which the services (typically) originate, such as a service provider network 118 and the Internet 120 and provide various subscriber services. Service provider network 118 and Internet 120 are commonly referred to as “core” networks.
The IP Network Element in existing networks generally will be one of either a Broadband Remote Access Server (BRAS) or an Edge Router (ER). Typical reference architectures use a BRAS for residential broadband deployments and ERs to provide business leased-line and single ended services, such as Internet access. Table 1 below summarizes the architectural differences between a BRAS, an ER, and proposed next-generation NEs, with the focus on traffic management capabilities.
TABLE 1FunctionBRASERNext GenerationApplicationResidential broadbandBusiness leased lineResidential broadbandnetworksMulti-service networksSubscriber facingATM, EthernetPDH (DS1, T3),Gigabit EthernetinterfacesEthernetTrunk/core facingEthernet, POS, GigabitEthernet, POS, Gigabit10 Gigabit EthernetinterfacesEthernetEthernetSubscriber/customerTunnels (PPPoA,Physical ports, timeslotDHCPidentificationPPPoE)or Layer 2 technique(e.g. VLAN, VPI/VCI,DLCI etc)Traffic typeNot ApplicableL2: VLAN/802.1p,L2 + L3 + L4 + applicationidentificationVPI/VCIL3: DSCP/TOSL4: SocketTraffic ManagementManaging subscriberManaging port and/orManaging servicefocustraffic (virtual stream)CoS traffic per porttraffic per subscriberTraffic ManagementFine: 1000's smallCoarse: 100's fatterFine: 10,000's queue,granularitypipespipessupporting both thinand fat pipesQueues1000's, per subscriberSmaller: ports × Cos100,000's, persubscriber × serviceQueue allocation policyFixed-per subscriberFixed-CoS based?   InnovationrequiredTM sophisticationLimited-ensure fairMore sophisticated-Sophisticated-ensureallocation of bandwidthensure prioritizationservice quality with abetween subscriberper portsubscriber and servicecategory
As broadband residential access networks evolve to deliver services other than HSI, the capabilities of the BRAS must extend to match. Similarly, ERs currently do not have the TM capabilities to handle thousands of subscribers, each demanding their own set of service queues. These evolving requirements are captured in the next generation column of Table 1.
From Table 1, it is clear that the area of TM requires the most significant changes. Typically BRAS devices lack the sophisticated service-aware traffic management functions to provide dedicated queues per service, per subscriber. Secondly, the requirement to have a dedicated queue per subscriber, irrespective of whether the subscriber is on-line and using the service fundamentally limits the number of subscribers an NE can provide.
The ER approaches the problem differently. If only a small number of queues per interface are supported, an aggregate queuing model must be employed. In this model, all service-specific traffic (e.g. all voice traffic destined to all subscribers) is funneled or aggregated through a single service specific queue. The number of queues required is thus limited to the number of discrete services supported by the network per port.
This model can only control the behavior of the aggregate queue (i.e. ensuring the aggregate bandwidth, aggregate packet loss, aggregate delay and jitter are sufficient), rather than the behavior of the constituent subscriber service flows. In this case, it is entirely possible (and likely) that although the aggregate quality of service is being meet, the quality of service for the individual subscriber service flows may not be satisfied.